1. Field of the Invention
The invention relates to a process and a facility to remove solid matter from an aqueous fibrous material suspension.
2. Discussion of Background Information
Processes of the above-discussed type are used to eliminate at least a portion of the undesired solid matter particles suspended in a fibrous material suspension containing fibrous material. It is known that a foam or scum containing the materials to be eliminated is formed in a floatation process. A common use of such a process is the preparation of an aqueous fibrous material suspension gleaned from printed recycled paper, in which the printing ink particles are already separated from fibers, so that they can be floated out. The flotation process described here utilizes the differences between fibrous material and undesired solid matter particles in such a way that the fibrous material remains in the fibrous material suspension due to its hydrophilicity, while the already-mentioned solid matter particles are hydrophobic and thus mix the foam with the air bubbles. Aside from printing ink particles, there are other materials which are hydrophobic and thus can be separated by flotation from the fibrous material. In particular, such materials are adhesives, fine synthetic material particles, and perhaps also resins. When fibers are separated from contaminations through the flotation process, not all solid matter particles are to be sorted out. Thus, selective flotation processes are performed. The term "flotation de-inking," likewise utilized, is generally not only used for the removal of printing ink particles but rather more generally for the selective flotation of contaminations from fibrous material suspensions.
The prior art with respect to flotation procedures for fibrous material suspensions has advanced quite far. Therefore, solutions exist which are certainly suited for removing a large portion of the interfering material particles by flotation. It is disadvantageous, however, that in many cases the separation distinction is insufficient; that is, too many fibers reach the foam with the contaminations. They then are either lost or must be retrieved through great effort.
The invention therefore has the fundamental task to create a flotation process with which losses of desired components, especially the fibers, are low with a simultaneously good removal effect of the undesired particles.